Binary Metallic Melts Research Articles

New Analyzing Approaches for In Situ Interdiffusion Experiments to Determine Concentration-Dependent Diffusion Coefficients in Liquid Al–Au

Interdiffusion coefficients are key parameters for the solidification process of liquid alloys. However, the determination of interdiffusion coefficients in liquid metals at high temperatures is a challenging and extensive task, due to a variety of potential systematic errors. In recent years we have developed an X-ray in situ shear cell method for the measurement of interdiffusion coefficients in binary metallic melts. This technique enables the monitoring of the experiment in order to exclude fatal errors. Utilizing X-ray contrast, the method also provides a time-resolved concentration distribution. Such an in situ data set contains significantly more information than ex situ evaluated experiments. Available analyzing strategies do not fully exploit this potential yet. We present three new analyzing approaches that are able to retrieve a concentration-dependent interdiffusion coefficient from only one in situ data set. In that way, larger concentration differences become accessible for an experiment, which considerably decreases efforts. Using simulations, the approaches are checked for robustness. Furthermore, the approaches are run on real in situ data from a binary (0 to 9 at% Au-content) Al–Au alloy at 1000 °C which results in a concentration-dependent interdiffusion coefficient within the measured concentration range.

Direct and Reverse Separation of Binary Metallic Melts in Capillaries

Direct and Reverse Separation of Binary Metallic Melts in Capillaries

To understanding of slow and non-monotonic relaxation in Al–Y eutectic melts

We discuss the nature of slow relaxation processes in glass-forming eutectic melts right after melting. For specific, we focus on the binary metallic melt Al–Y, which in addition to the slow relaxation shows unusual non-monotonic dynamics. We argue this slow dynamic the result of non-linearity of diffusion processes in the initially non-homogenous sample, and the nature of slow relaxation processes in eutectic melts after melting is similar to the nature of spinodal decomposition when the reason for the slowdown is the thermodynamic instability. To support this assertion we considered the model with combined Gibbs potential of the Al-Y liquid solution, in which the presence of the stoichiometric phase remains is taken into account. We show that in this system the instability mathematically described by the Cahn–Hilliard type equation can develop, and that fluctuation accounting in the considered model allows qualitatively describe the non-monotonic relaxation observed in the Al-based non-equilibrium melts.

Viscous properties of nickel-containing binary metal melts

The paper presents the results of molecular dynamics study of the viscosity of nickel-containing binary metal melts for a wide range of temperatures, including the region of the equilibrium liquid phase and supercooled melt. It is shown that the temperature dependencies of the viscosity of binary metal melts are described by the Kelton’s quasi-universal model. Based on the analysis of the viscosity coefficient of the binary melt composition within the framework of the Rosenfeld’s scale transformations, it has been established that to correctly describe the viscosity of binary/multicomponent metal melts within the framework of entropy models, it is necessary to use a more complex representation of the excess entropy S ex than in the approximation of pair correlation entropy S 2.

Stratification of In–Bi Melts in Glass Capillaries

The stratification of binary metal melts in glass capillaries was studied over the whole concentration range of the indium–bismuth system. The results of stratification were correlated with the form of the state diagram and other physicochemical properties of the melts, especially with the isobaric heat capacity. The value of the achieved difference in the concentrations of the components along the capillary height is related to the balance between the clusters (units) of pure components and their chemical compounds presented in the state diagram of the binary system. The depth of stratification of the melts in the field of chemical compounds is much smaller than in the “eutectic zones” of the diagram. The intermetallic compounds InnBim retained their stability when overheated above the liquidus line by at least 300°C. The results of our study of stratification in capillaries are characterized by high sensitivity with respect to the density of the clusters located directly in the metal melts and are structure-sensitive, due to which they may be recommended for use as one of the physicochemical techniques for investigating the structure of liquid metal alloys.

Модель микрокристаллизации 50 % двухкомпонентных металлических расплавов в диффузионно-релаксационном режиме

Рассмотрена модель микрокристаллизации 50% двухкомпонентных металлических расплавов в диффузионно-релаксационном режиме. При этом развита модель переходной двухфазной зоны (ПДЗ) в пространстве концентраций мономеров роста, принадлежащих двум агрегатным состояниям – расплаву и кристаллу. Записаны кинетические дифференциально-разностные уравнения, описывающие эволюцию структуры ПДЗ во времени с учетом ее «ступенчатой» формы, образованной механизмом спонтанных флуктуаций с ограниченным спектром изменения концентраций мономеров роста (в модели ПДЗ) во всех монослоях переходной конечной области, отделяющей собой двухкомпонентный расплав от кристаллической фазы. Учтены зависимости частот обмена мономерами роста между расплавом и кристаллом от энергий связи двух ближайших мономеров и от температуры кристаллизующейся системы расплав-кристалл. Эта модель соответствует схеме реальной конечной протяженности поверхности раздела двух соприкасающихся фаз и носит название кристалла Косселя-Странского.
 
 
 ЛИТЕРАТУРА
 
 Baikov Yu. A., Petrov N. I. Russian Physics Journal, 2014, vol. 57, no. 4, pp. 459-468. https://doi.org/10.1007/s11182-014-0262-2
 Baikov Yu. A., Petrov N. I. Russian Physics Journal, 2014, vol. 57, 5, pp. 598-614. https://doi.org/10.1007/s11182-014-0282-y
 Baikov Yu. A., Petrov N. I. Russian Physics Journal, 2014, vol. 57, no. 4, pp. 459-468. https://doi.org/10.1007/s11182-014-0262-2
 Baikov Yu. A., Petrov N. I. Russian Physics Journal, 2014, vol. 57, no. 5, pp. 598-614. https://doi.org/10.1007/s11182-014-0282-y
 Baikov Yu. A., Petrov N. I. Vestnik of MGOU, ser. "Physics and Mathematics", 2014, no. 2, p. 63. URL: https://www.vestnik-mgou.ru/Articles/Doc/7435 (in Russ.)
 Petrov N. I. The Crystal Disordering Study When Growing From the Binary Metallic Melts. National University of Science and Technology «MISiS» Dis. Cand. Phys. - Mat. Sci. Moscow, 2017, 180 p. URL: http://misis.ru/files/6902/Petrov_AR.pdf (in Russ.)
 Sarkisov P. D., Baikov Yu. A., Meshalkin V. P. The One – and Binary Metallic Melts Mathematical Modeling Crystallization. Moscow, Physmatlit Publ., 2003, 378 p. URL: https://istina.msu.ru/publications/book/101828661/ (in Russ.)
 Sarkisov P. D., Baikov Yu. A., Meshalkin V. P. Collection of Works. “The Optimization of Composition, Structure and Properties of Metals, Oxides, Composites, Nano – and Amorphous Materials”, Russia-Israel Conference, Moscow – Yekaterinburg, 2002, p. 172. URL: https://istina.msu.ru/publications/article/103469568/
 Sarkisov P. D., Meshalkin V. P., Baikov Yu. A. Collection of Works. “The Optimization of Composition, Structure and Properties of Metals, Oxides, Composites, Nano – and Amorphous Materials”, Russia-Israel Conference, Moscow – Yekaterinburg, 2002, 184. URL: https://istina.msu.ru/publications/article/103469593/
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Влияние температуры на скорость расслоения расплавов Sn-Pb в капиллярах

Проведено исследование влияния температуры на скорость процесса расслоения металлического расплава олово-свинец в наклонном стеклянном капилляре. Основной целью исследования является установление механизма расслоения металлов. Температура считается одним из основных параметров молекулярно-кинетического движения атомов конденсированной системы частиц в жидком состоянии. Скорость движения атомов или кластеров должна определять скорость самого процесса расслоения, если он связан с диффузионными или конвекционными явлениями в системе. Эксперименты показали, что с высокой степенью вероятности температура не влияет на динамику переходных кривых, что указывает на особый механизм этого эффекта, не связанный напрямую с общепринятыми молекулярно-кинетическими закономерностями.
 
 ИСТОЧНИК ФИНАНСИРОВАНИЯ
 Исследование выполнено при финансовой поддержке РФФИ, проект № 16-01-00662а.
 
 
 ЛИТЕРАТУРА
 
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 Uglev N. P., Uglev S. N. Rasplavy, 2018, no. 4, pp. 411-419. https://doi.org/10.1134/s023501061804014x 
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Separation of Low-Melting Metal Melts in a Thin Inclined Capillary

Direct numerical simulation of the process of separation of binary low-melting metal melts in a thin nonuniformly heated inclined capillary is carried out. A physical model which describes the macroscopic motion in the melt and the process of separation of the liquid mixture in components is constructed on the basis of laws and equations valid for the multiphase hydrodynamic systems. The calculation results are compared with the experimental data. The separation time is compared for various angles of inclination of the layer, the characteristic concentration fork which demonstrates separation dynamics is reproduced, and the qualitative agreement with the experiment is obtained for the component concentrations in the cross-section. In the course of numerical simulation, that replicates the succession of experimental actions with the maximum precision, the presence of the specific maximum for the difference between the end-face concentrations at a certain angle of inclination of the channel is confirmed. The radical difference between the calculation results obtained within the framework of the model considered and the conclusions made earlier in explanation of the experiment by other authors is demonstrated.

Effect of component substitution on the atomic dynamics in glass-forming binary metallic melts

We investigate the substitution of early transition metals (Zr, Hf, and Nb) in Ni-based binary glass-forming metallic melts and the impact on structural and dynamical properties by using a combination of neutron scattering, electrostatic levitation (ESL), and isotopic substitution. The self-diffusion coefficients measured by quasielastic neutron scattering (QENS) identify a sluggish diffusion as well as an increased activation energy by almost a factor of 2 for Hf35Ni65 compared to Zr36Ni64. This finding can be explained by the locally higher packing density of Hf atoms in Hf35Ni65 compared to Zr atoms in Zr36Ni64, which has been derived from interatomic distances by analyzing the measured partial structure factors. Furthermore, QENS measurements of liquid Hf35Ni65 prepared with 60Ni, which has a vanishing incoherent scattering cross section, have demonstrated that self-diffusion of Hf is slowed down compared to the concentration weighted self-diffusion of Hf and Ni. This implies a dynamical decoupling between larger Hf and smaller Ni atoms, which can be related to a saturation effect of unequal atomic nearest-neighbor pairs, that was observed recently for Ni-rich compositions in Zr-Ni metallic melts. In order to establish a structure-dynamics relation, measured partial structure factors have been used as an input for mode-coupling theory (MCT) of the glass transition to calculate self-diffusion coefficients for the different atomic components. Remarkably,MCT can reproduce the increased activation energy for Hf35Ni65 as well as the dynamical decoupling between Hf and Ni atoms.

General equation describing viscosity of metallic melts under horizontal magnetic field**Project supported by the National Natural Science Foundation of China (Grant No. 51371107).

Viscosities of pure Ga, Ga80Ni20, and Ga80Cr20 metallic melts under a horizontal magnetic field were investigated by a torsional oscillation viscometer. A mathematical physical model was established to quantitatively describe the viscosity of single and binary metallic melts under a horizontal magnetic field. The relationship between the viscosity and the electrical resistivity under the horizontal magnetic field was studied, which can be described as (ηB is the viscosity under the horizontal magnetic field, η is the viscosity without the magnetic field, H is the height of the sample, Ω is the electrical resistivity, and B is the intensity of magnetic field). The viscosity under the horizontal magnetic field is proportional to the square of the intensity of the magnetic field, which is in very good agreement with the experimental results. In addition, the proportionality coefficient of ηB and quadratic B, which is related to the electrical resistivity, conforms to the law established that increasing the temperature of the completely mixed melts is accompanied by an increase of the electrical resistivity. We can predict the viscosity of metallic melts under magnetic field by measuring the electrical resistivity based on our equation, and vice versa. This discovery is important for understanding condensed-matter physics under external magnetic field.

Electrotransport in binary iron-based metal melts

The mobility of ions in binary iron-based liquid metal systems is calculated for the first time, based on studies on the specific resistance and self-diffusion coefficient in a wide range of concentrations. It is established that iron ions move toward the anode in Fe–V and Fe–Mo systems, and toward the cathode in Fe–W and Fe–Pt systems; i.e., there is inversion of electrotransport for iron ions. When the concentration of a component is reduced, the mobility of its ions grows in modulus.

Surface tension of lead–bismuth eutectic melts with lithium

The temperature and concentration dependences of the surface tension of lithium alloys (up to 33.1 at %) on the basis of a eutectic melt of Pb44.7Bi55.3 are measured in the range from the liquidus temperature to 700 K. The margin of error of the experiments was ~2%. Lithium has a low surface activity in the Pb44.7Bi55.3 eutectic melt, which agrees with the criteria of the surface activity of components in binary liquid metal melts.

Influence of the Marangoni–Gibbs effect on the separation of binary metallic melts in capillaries

The separation of the tin and lead melts at an artificially maintained temperature gradient along the capillary length is studied. Direct experiments demonstrate that the separation rate and the component concentration difference along the capillary length remain unchanged at any gradient direction for vertical, inclined, and horizontal capillaries. These results show that the Marangoni–Gibbs effect weakly affects the melt separation.

An equation describing diffusivity of liquid atoms by magnetic confinement

In this work, we report an obvious low field-induced magnetic confinement effect on the diffusivity in binary metallic melts under a weak magnetic field. A quantitative description of this nontrivial dynamic behavior is given by a physical analytical model based on the Hall effect, which is in agreement with our experimental results. Meanwhile, a quadratic B dependence of the dynamic viscosity obtained in the same confined environment is observed. Our results show that one can effectively control the atomic diffusion process of metallic melts by the application of magnetic field. Meanwhile, this magnetic confinement effect at atomic scale should provide an important new ingredient to deeply understand the condensed matter physics under the external magnetic field.

Diffusion and interdiffusion in binary metallic melts

We discuss the dependence of self- and interdiffusion coefficients on temperature and composition for two prototypical binary metallic melts, Al-Ni and Zr-Ni, in molecular-dynamics computer simulations and the mode-coupling theory of the glass transition (MCT). Dynamical processes that are mainly entropic in origin slow down mass transport (as expressed through self-diffusion) in the mixture as compared to the ideal-mixing contribution. Interdiffusion of chemical species is a competition of slow kinetic modes with a strong thermodynamic driving force that is caused by nonentropic interactions. The combination of both dynamic and thermodynamic effects causes qualitative differences in the concentration dependence of self-diffusion and interdiffusion coefficients. At high temperatures, the thermodynamic enhancement of interdiffusion prevails, while at low temperatures, kinetic effects dominate the concentration dependence, rationalized within MCT as the approach to its ideal-glass transition temperature ${T}_{c}$. The Darken equation relating self- and interdiffusion qualitatively reproduces the concentration dependence in both Zr-Ni and Al-Ni, but quantitatively, the kinetic contributions to interdiffusion can be slower than the lower bound suggested by the Darken equation. As temperature is decreased, the agreement with Darken's equation improves, due to a strong coupling of all kinetic modes that is a generic feature predicted by MCT.

Surface tension of melts of binary alkali element systems: The sodium-cesium system

Experimental data are presented for the surface tension of melts of the sodium-cesium system in the liquid state, obtained by the large drop method on samples prepared from high-purity components. It is shown that cesium in melts exhibits very high surface activity, attaining in extreme cases ∼3000 mN/(m at %). Our results verify data of the activity ratio of cesium in melts with sodium and correlates with the basic criteria for surface activity in binary metal melts.

Stokes–Einstein relation in dense metallic glass-forming melts

Quasielastic neutron scattering has been used to investigate atomic motion in a very fragile binary metallic melt and a multicomponent bulk glass-forming metallic melt. Both melts show a breakdown of the Stokes–Einstein relation and display a change in the slope of In D dependence on In(η/T). We also observed that the values for the exponent in the fractional Stokes–Einstein relation are not in the commonly observed range for Cu46Zr42Al7Y5 melts. At low temperatures, the deviation from the Stokes–Einstein law is very significant and can be expressed in the form of a power law with exponent ξ=−1.82±0.08. The change in the slope is found to be associated with a change in friction coefficient while increasing the packing density of the melt. The abrupt change in the value of friction coefficient is independent of packing density, but it occurs at a common value of ζ=(3.2±0.1)×10−12 kg s−1 in these melts.

Geometrical aspects of the glass-forming ability of dense binary hard-sphere mixtures

Non-crystalline dense binary hard-sphere mixtures are generated where the size ratio of the spheres and the fraction of small spheres are varied from 1.0 to 2.0 in steps of 0.1 and from 0 to 100% in steps of 10%, respectively. A confined region within this parameter space is defined where non-crystalline structures are stabilized. Comparison of the present results with experimental data for binary bulk metallic glasses supports the validity of geometrical arguments regarding glass-forming ability of binary metallic melts.

Mathematical model of a stratification of metal melts in capillaries

The partial stratification of binary metal melts in crucibles during centrifuging, or in capillaries under influence of gravity, as yet has no consistent explanation within the framework of the existing theories of liquid state. The mathematical model of the stratification process based on assumed special properties of mononuclear skin (interphase layer) of a melt describing satisfactorily all experimental results on stratification of metals in capillaries is proposed.

Marco- and microseparation in Ga-Pb melts

A procedure for the separation of the contributions of two liquid phases making up a binary metallic melt with a miscibility gap to its diffraction pattern is proposed. The simulation of the structures of two such liquids in the Ga-Pb system indicates that they are qualitatively different: the liquid phase based on the component with a lower melting point is microinhomogeneous, and the liquid based on the component with a higher melting point exhibits a virtually statistical atomic distribution.